The present invention relates to flashlamps, and more particularly to a flashlamp that provides simple manufacturability, ruggedized operation, high average output power, and long life.
A flashlamp (sometimes referred to as a "flash tube") is a device that produces a brief burst of light because of the ionization of a gas. A flashlamp includes a glass tube (or other quartz envelope) filled with a gas, e.g., xenon, at low pressure, and two electrodes, one at each end of the tube. In some embodiments, the tube may be coiled to increase its length while minimizing its occupied volume, in order to provide a brighter flash. When a sufficiently high voltage is momentarily applied between the electrodes, the gas in the tube ionizes and produces a flash of light.
Advantageously, the flash of light produced by a flashlamp or flash tube may be controlled to occur at a precise instant of time, determined by when the voltage is applied to its electrodes. A flashlamp may thus be controlled to "flash" for a single flash, or for multiple flashes, at an irregular or periodic rate, which rate may be very rapid. Flashlamps are commonly used in strobe lights. Flashlamps are also frequently used in photography, and any other application where a bright burst of light is needed at a particular timed instant or interval. Flashlamps also find common use in processing facilities, e.g., to perform biological sterilization, as in a food processing facility. Flashlamps may also be used to cure some epoxies, and in ultraviolet photolithography.
One of the difficulties encountered with flashlamps of the prior art relates to maintaining a proper seal between the glass tube and the metal electrodes at each end of the tube. Flashlamps have thus fallen into two basic design categories: (1) those employing a "hard" glass to metal seal; and (2) those employing a soft solder glass to metal seal. The first type of flashlamp requires the skill of a glass blower, is extremely difficult to manufacture uniformly, and is inherently fragile. Further, this first type of flashlamp is unduly limited in its average power handling capability because the heat dissipated in the electrode must be extracted through the glass tube.
The second type of flashlamp is more "rugged" than the first (i.e., not as fragile), and offers somewhat improved average power handling capability because of additional thermal conductivity at the electrode ends where the solder seal is made. This additional thermal conductivity provides a thermal path through which much of the heat developed during operation of the lamp may be dissipated. Nonetheless, the second type of flashlamp, along with the first type of flashlamp, suffer from some common deficiencies. For example, it is not possible to clean the lamp, i.e., clean the inside of the glass tube or other quartz envelope, once the final sealing operation, e.g., welding or soldering, has taken place. Further, both types of design suffer from a serious design flaw that prevents optimum performance and long life. This flaw results because the electrodes must be brazed onto a suitable support stem. Such brazing causes contamination at the electrode. Hence, the electrode can never have the purity of the pristine electrode material. Disadvantageously, any contaminants present at the electrode, e.g., as introduced through brazing, are eventually manifest as deposits on the inside of the glass tube or other quartz envelope. Such deposits not only limit the amount of light that can be transmitted through the glass or quartz material (i.e., they cloud up the inside of the flashlamp), but they also adversely affect the thermal properties of the glass or quartz material, which eventually may cause the glass or quartz tube to break. In either event, the presence of any contaminants at the electrode has the effect of shortening the useful life of the flashlamp.
In view of the above deficiencies, it is evident that there is a need for a flashlamp that is easy to manufacture; provides improved thermal conductivity to allow higher average power dissipation therein; allows cleaning of the quartz envelope; and eliminates the need to braze the electrode to a support stem, thereby maintaining the purity of the electrode material and increasing the useful operating life of the flashlamp. The present invention advantageously addresses the above and other needs.